1,3-bis(trimethylsilyl)urea

Melting point / freezing point

Link to relevant study record(s)

Reference

Endpoint:

melting point/freezing point

Type of information:

experimental study

Adequacy of study:

key study

Study period:

22 Jul to 20 Dec 2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 102 (Melting point / Melting Range)

Qualifier:

according to guideline

Guideline:

EU Method A.1 (Melting / Freezing Temperature)

GLP compliance:

yes (incl. QA statement)

Remarks:

Medicines & Healthcare products Regulatory Agency (MHRA)

Type of method:

differential scanning calorimetry

Decomposition:

yes

Decomp. temp.:

> 127 - < 258 °C

Results

Thermographic Data

Thermal event	Interpretation	Temperature (°C)
Endotherm		Determination 3	Determination 4
	Onset of decomposition	127.65	126.95
	Extrapolated onset of decomposition	234.23	235.37
	Endset of decomposition	257.07	258.48

 

Overall result: Decomposition occurred from approximately 127 to 258 °C (400 to 531 K)

 

Discussion

The Certificate of Analysis and safety data sheet indicated that the test item melted at 228 °C and 225 to 230 °C respectively. Therefore, the two initial determinations were performed over a narrow temperature and at a slow heating rate. However, although both determinations contained a broad endotherm, their profile and temperature at which they occurred was inconsistent. Both contained no residue.

 

Two further determinations were performed to evaluate the phase transition over a much wider temperature range (20 to 400 °C) and faster heating rate. Again, both contained no residue but this time were consistent and showed more thermographic detail.

 

Three informational runs showed that the residue was still a white powder after being heated to 220 °C but was a white solid around the periphery of the crucible by 240 °C. This latter observation suggests the test item had at least partially liquefied between 220 and 240 °C and attributed to the melting temperature stipulated on the Certificate of Analysis. However, the three informational runs had weight losses of 9% (180 °C) 32% (220 °C) and 83% (240 °C) which showed the test item was volatising as the temperature increased. For determinations 1 and 2 that had been heated to 260 °C there was a loss of 100%.

 

It was concluded that the test item had not melted but rather decomposed at an increased rate as the temperature increased. There was a point where the mixture of test item and decomposition products began to liquefy, but ultimately further decomposed and completely evaporated. The liquid phase was therefore short lived and the temperature at which it occurred may change depending on the heating rate. This melting stage also indicated that the thermal event was not the test item subliming.

 

The thermographic baseline for all four determinations also indicated an evaporative event rather than melting. This is because there is a shift in the baseline before the main thermal event and with the baseline after the event. This occurs when the thermal capacity of the crucible changes due to loss of its contents, which is unlike that for a melting event where no content is lost so the thermal capacity remains the same and the baseline is at the same level before and after the event.

 

As a result of the initial low rate of enthalpy change during decomposition, the onset temperature could only be approximated.

 

Six small endothermic events were also integrated in the thermograms for determinations 3 and 4 which may have been the phase transition of minor component or impurities. They occurred at approximately 131, 139, 156, 172 and 187 °C. These were not used to evaluate the test item as whole.

 

Conclusion

The test item was determined to decompose from approximately 127 to 258 °C (400 to 531 K). As the test item decomposed, no value for melting point could be determined

Description of key information

No melting point, the substance decomposed before melting (OECD 102, differential scanning calorimetry)

Additional information

Decomposition occured from approximately 127 to 258 °C